The invention concerns a device for blowmolding a thermoplastic material, which includes a heating device for tempering preforms and a blow device for blowmolding the preforms into a container, and in which at least one preloadable control disk is provided for triggering at least one blow station located in the region of the blow device.
Such devices are used, for example, in order to mold preforms, especially preforms made of polyethylene, into containers. For tempering of the preforms heating elements are provided in the region of the heating facility, which emit the energy tempering the preform. After they are tempered, the preforms are transferred to the blow device, and are there, in the region of blow stations, formed into containers. Especially in the case of blow devices in the form of blow wheels,.control disks are used, which, in combination with carrier disks and depending on their rotational positioning, supply pneumatic elements in the region of the blow station with working air. For this purpose groove-shaped recesses are provided in the area of the control disk, which are developed partly to carry pressure and partly to exhaust pressure. Along the groove-shaped recesses holes are drilled in the region of the carrier disk, and via these drillings working pressure is conveyed to the pneumatic elements, or compressed air conveyed to the pneumatic elements is exhausted. To ensure compact construction the control disk is sealed against the carrier disk by a relatively thin, planar gasket. To ensure a sufficiently reliable seal, the control disk is pre-loaded with regard to the carrier disk. The pre-load can occur, for example, in such a way, that the control disk is fixed and the carrier disk is positioned rotatably relative to a center column. In the region of its extension away from the control disk, the carrier disk is equipped with a spring holding it against the control disk. For the design of such a spring it is known to use mechanical spring elements, for example, disk springs.
The use of such disk springs has the disadvantage, that in order to allow the possibility of movement of the carrier disk relative to the control disk and thus to allow the possibility of positioning the blow wheel in a maintenance or service operation, a counter force compensating for the spring force of the disk spring has to be generated by way of a pneumatic supply. This has the consequence that a pressureless operation of the device is not possible. Especially in the case of problems in the region of the machine or for carrying out service- or adjustment work, working without pressure is desirable to avoid danger to persons working near the device.
The use of mechanical spring elements has further the disadvantage that during assembly tensile forces have to be generated which increase the assembly cost.
It is the task of the present invention, therefore, to improve a device of the introductorily named type in such a manner, that the assembly and service qualities are improved.
In accordance with this invention the problem is solved, in that the control disk is preloadable vis-a-vis a carrier disk by at least one pneumatic spring is connected to a pressure release device allowing pressure-free maintenance operations.
The use of a pneumatic spring makes it possible, to divert the pre-load force of supply pressure to be distributed. When the supply pressure is removed then the spring force is removed at the same time. In the case of performing maintenance in the absence of pressure it is thus possible to perform rotational movements in the region of the blow wheel without compensating for the mechanical pre-load forces. The use of a pre-load device in the form of a pneumatic spring has the further advantage, that for the assembly no pre-load forces need to be generated. The elements of the pneumatic spring can rather be assembled with introduction of a significant force and the pre-load forces are not provided until the start of operation after actuation of the supply pressure.
According to a preferred embodiment of the invention it is proposed that the pneumatic spring is formed at least one piston covered with a membrane. Such membranes are especially suited for carrying out short stroke adjustment motions and facilitate the positioning of a piston, which transmit the pre-load to the carrier disk.
According to another preferred embodiment provision is made that the piston is formed as an annular piston which is arranged essentially concentric with the axis of motion of the carrier disk. By forming it as an annular piston it is assured that in spite of a relatively simple drive a large pressure surface is provided and thus an effective power transmission is made possible.
According to a further preferred embodiment, the assembly and maintenance properties are additionally improved, in that a two step pressure reducer is used for adjusting the supply pressure. The two step construction makes it possible to make a preadjustment by means of pressure regulator, which, for example, is equipped with a handwheel, which is then used for the adjustment of the main pressure regulator. Hitherto required extensive mechanical adjustment efforts are thus avoided.
A further improvement of the assembly properties is achieved in that at least in the region where transfer elements connect the heating device with the blow device, torsionally stiff couplings are provided. The use of such couplings has the advantage that an assembly with relatively large tolerances can be carried out and deviations regarding tilt and a mismatch in the region of rotational shafts can be compensated.
Further details of the present invention emerge from the subsequent detailed description and the attached drawings, in which, for example, preferred embodiments of the invention are shown.